Process for synthesizing sucrose esters of fatty acids

ABSTRACT

THE IMPROVED PROCESS FOR SYNTHESIZING SUCROSE ESTERS OF FATTY ACIDS COMPRISES THE STEPS OF; (A) PREPARING A SOLUTION OF THE MIXTURE OF SUCROSE AND A FATTY ACID SOAP WITH WATER, SAID SUCROSE BEING COMPLETELY DISSOLVED IN SAID SOLUTION; (B) ADDING TO SAID SOLUTION OF THE MIXTURE A FATTY ACID ESTER AND A CATALYST FOR THE TRANSESTERFICATION REACTION BETWEEN SUCROSE AND SAID FATTY ACID ESTER UNDER SUCH TEMPERATURE ELEVATING SAID PRESSURE REDUCING CONDITIONS AS TO AVOID HYDROLYSIS OF SAID FATTY ACID ESTER IN THE ORDER TO FORM A SUBSTANTIALLY COMPLETELY DEHYDRATED, HOMOGENEOUS MELT COMPOSITION; AND (C) CARRYING OUT THE TRANSESTERIFICATION REACTION BETWEEN SUCROSE AND SAID FATTY ACID ESTER IN SAID MELT COMPOSITION AT A TEMPERATURE WITHIN THE RANGE OF 110* TO 175*C.

A WMMWQQQ O 0 0 0 w w m w m w a\ 1 D Filed 001;. 23, 1970 20 W47R CONTNT FUMIAKI YAMAGISH! EI'AL PROCESS FOR SYNTHESIZING SUCROSE ESTERS OF FATTY ACIDS Feb. 12, 1914 United States Patent Office 3,792,041 Patented Feb. 12, 1974 Int. Cl. 69/32 US. Cl. 260-234 R Claims ABSTRACT OF THE DISCLOSURE The improved process for synthesizing sucrose esters of fatty acids comprises the steps of:

(a) preparing a solution of the mixture of sucrose and a fatty acid soap with water, said sucrose being completely dissolved in said solution;

(b) adding to said solution of the mixture a fatty acid ester and a catalyst for the transesterification reaction between sucrose and said fatty acid ester under such temperature elevating and pressure reducing conditions as to avoid hydrolysis of said fatty acid ester in order to form a substantially completely dehydrated, homogeneous melt composition; and

(c) carrying out the transesterification reaction between sucrose and said fatty acid ester in said melt composition at a temperature within the range of 110 to 175 C.

BACKGROUND OF THE INVENTION This invention relates to a process for synthesizing sucrose esters of fatty acids. In particular, this invention relates to a process for synthesizing sucrose esters of fatty acids in a relatively short period of time, with a high yield and in an industrially available manner, wherein sucrose esters of fatty acids are produced through the formation of a homogeneous, dehydrated melt composition of reactants under such temperature and pressure conditions as to cause no hydrolysis of fatty acid ester materials and employing a flux and water as a solvent.

Among various food additives, sucrose esters of fatty acids are highly estimated for their high hydrophilic property and strong emulsifying effect. In conventional processes for the production of sucrose esters of fatty acids on an industrial scale, dimethyl formaldehyde is used as a solvent for carrying out a reaction between sucrose and a fatty acid. This process is hereinafter referred to as DMF process. Belgian Pat. No. 696,700 granted to Osipow et al. discloses an improved process for the production of sucrose esters of fatty acids utilizing a transparent emulsion. This process is known as the transparent emulsion process.

However, the DMF process is disadvantageous in that it utilizes a poisonous solvent and the complete removal of the solvent is extremely difficult.

According to the transparent emulsion process, a sucrose ester of fatty acid is synthesized from sucrose and a fatty acid utilizing propylene glycol as a solvent and a surfactant as an emulsifier. This process is characterized in the formation of microemulsion of the reactants. The transparent emulsion process is also attended by various problems which have been hindering this process from being industrialized. The most serious problems are that the micro-emulsion has such a low stability as to make the control of reaction conditions very diflicult in the industrialized stage, that the process requires a high vacuum and an extended reaction time since the solvent used has a relatively high boiling temperature, and the obtained product is of a lower quality because the separation of the emulsifier from the obtained sucrose ester of fatty acid by a purification process is difficult.

The primary object of the invention is to provide a new and improved process for synthesizing sucrose esters of fatty acids with an increased yield, in a relatively short period of time, and in an industrially available manner.

Another object of the invention is to provide a new and improved process for synthesizing sucrose esters of fatty acids in which sucrose esters of fatty acids are synthesized from a dehydrated, homogeneous melt composition of reactants.

A further object of the invention is to provide a new and improved method for obtaining a dehydrated, homogeneous melt composition of reactants from which sucrose esters of fatty acids are synthesized, wherein the preparation of the melt composition of reactants is carried out with use of water as a solvent and a particular flux in such a manner that hydrolysis of esters of fatty acids can be prevented.

SUMMARY OF THE INVENTION According to the invention the improvement in the process for synthesizing sucrose esters of fatty acids in which sucrose esters are produced by a transesterification reaction between sucrose and fatty acid esters comprises the following steps of:

(a) preparing a solution of the mixture of sucrose and fatty acid soap with water, sucrose being completely dissolved in said solution;

(b) adding to said solution of the mixture a fatty acid ester and a catalyst for the transesterification reaction between sucrose and said fatty acid ester under such temperature elevating and pressure reducing conditions as to avoid hydrolysis of said fatty acid ester in order to form a dehydrated, homogeneous melt composition; and

(c) carrying out the transesterification reaction between sucrose and said fatty acid ester at a temperature within the range of to C.

Preferably, the fatty acid ester is added only at step (b), although a remaining amount of the fatty acid ester may be added at the step (c) after the substantial amount thereof is added at the step (b).

The step (c) is preferably carried out under reduced pressure but it may also be carried out at atmospheric pressure.

According to this invention, since water is used as the solvent, sucrose is readily dissolved and only a small amount of water is required for forming a solution containing sucrose in a completely dissolved state. The water used as the solvent is removed from the system during the step of forming the dehydrated, homogeneous melt composition. Thus, the present process does not require a separate additional step for recovering the solvent which is indispensable with the DMF process or the transparent emulsion process. Moreover, the present process is entirely free from the problems arising from the fact that an amount of a poisonous solvent may remain in the final product of the DMF process or from the presence of by-produced propylene glycol esters in the final product of the transparent emulsion process wherein propylene glycol is used as the solvent. In addition, as will be described hereinafter in detail, the formation of the homogeneous melt composition and subsequent reaction operation in the process of the invention are effective in reducing the amount of reaction by-products to a minimum, which results in producing sucrose esters of fatty acids having a high purity.

In order to obtain a homogeneous melt composition, it is necessary to stir the system. In the process of the invention, although water is removed from the system the viscosity of the system is not so extremely increased because the operation is carried out at a relatively high temperature in addition to the fact that a fatty acid soap is added. Thus, the well-known mechanical stirring operation may readily be employed in the process for obtaining the homogeneous melt composition.

Generally, in order to make a sucrose melt from sugar powder, sucrose must be heated up to a temperature above 140-145 C. at which sucrose begins to be softened. However, as the temperature of the heated sucrose approaches the above mentioned softening temperature, fine sucrose particles begin to aggregate. In addition, it is difficult to melt sucrose without causing thermal cracking and the sucrose melt obtained is thermally so unstable that it is readily decomposed and shows a poor afiinity to fatty acid esters. For the purpose of preventing the aggregation of the powdery sucrose, it has been found that fatty acid soaps may best be used as an anti-aggregation agent. The fatty acid soap acts also as a flux to reduce the temperature at which a melt composition is formed. The use of fatty acid soap is also advantageous in that it shows a good afiinity to both sucrose and fatty acid esters. If other materials than fatty acids soap, for example, sucrose esters of fatty acids are employed as the flux undesirable saponification occurs in such a high rate as 30 to 40%.

By the use of a fatty acid soap according to the invention it becomes possible to obtain a molten composition essentially comprising sucrose and a fatty acid ester in a stable state as well as in an economical manner.

The use of water as the solvent in the process of the invention provides many outstanding advantages as described above. However, cares must be taken to prevent the hydrolysis of fatty acid esters which may occur due to the use of water.

In general, esters are approximately quantitatively hydrolyzed in about 60 minutes in the presence of water and an alkali substance and at a temperature between 60 and 80. However, according to the invention, the solution of the mixture of sucrose and fatty acid soap with water is stable owing to the presence of the fatty acid soap, and, accordingly, water in the solution is not so easily freed to cause hydrolysis of fatty acid ester. Dehydration of the solution in which water molecules are stably combined with sucrose molecules can only be made by application of an elevated temperature and a reduced pressure.

In addition, we have found an unexpected fact that if the temperature elevation and the pressure reduction during the step of forming a dehydrated melt composition of reactants are properly controlled according to the rate of performance of dehydration, hydrolysis of fatty acid esters can be successfully avoided even at such high temperatures within the range of 100 to 160 C. and even in the presence of water as the solvent and an alkaline material as the catalyst for the transesterification reaction.

Conditions of avoiding the hydrolysis of fatty acid esters depend on and are related to various factors. Among these factors, the following may be mentioned: (1) the ratio of the amount of sucrose to that of fatty acid ester to be used, (2) the kind and amount of fatty acid soap to be used, (3) the kind of the catalyst and the amount of its use, (4) water content in the system forming the melt composition, (5) temperature and (6) pressure.

The rate of the amount of sucrose to that of a fatty acid ester should be within the range of 80:20 to 5:95 in weight.

Fatty acid soap may be K, Na or Ca salts of fatty acids having 8 to 22 carbon atoms and it may be used in an amount of 5 to 40% by weight with respect to the total amount of sucrose and fatty acid ester to be employed.

Any of alkaline materials which have been conventionally employed as the catalyst for an esterification reaction may also be used as the catalyst for the transesterification reaction between sucrose and fatty acid ester in the process of this invention.

Among those alkaline materials which can be used as the catalyst in the process of the invention, there may be mentioned hydroxides, carbonates, bicarbonates, methylates, ethylates and propylalcoholates of potassium, sodium and lithium. Potassium salts such as KOH, K CO are particularly preferred. The catalyst may be employed in an amount of 0.1 to 10% by weight of the amount of sucrose to be used.

In accordance with this invention, the catalyst is added to the system at any time after the solution of the mixture of sucrose and a fatty acid soap with water is prepared and before the formation of the dehydrated melt composition is completed.

Water may be used to make up the solution including sucrose and fatty acid soap in an amount of 10 to 200% by Weight with respect to the total amount of sucrose and fatty acid soap.

In order to obtain a dehydrated melt composition of reactants without causing hydrolysis of fatty acid esters, with the above described specific conditions for factors (1) to (3), the temperature and the pressure must be changed and controlled according to the dehyration rate during the step of forming the melt composition, within the specific ranges, respectively. Such specific ranges for the temperature and the pressure are given in Table 1.

TABLE 1 Water content (percent by weight) 20 15 10 5 0 Temperature C.) 70-110 75-135 -160 -165 175 Pressure (mm. Hg) 760-360 760-210 760-110 660-60 60-0 wherein X is the water content percentage in said melt composition, Y is the temperature in C. and Z is the pressure in mm. Hg.

BRIEF DESCRIPTION OF THE DRAWINGS A more complete understanding the relations between the water content and the temperature, and, between the water content and the indicated pressure which are indicated in Table 2 will be obtained from the following description with reference to the drawings in which:

FIG. 1 is a graphical illustration showing the critical range of the temperature according to the water content or dehydration rate during the step of forming a dehydrated melt composition in accordance with the invention; and

FIG. 2 is a graphical illustration showing the critical range of the pressure according to the water content or dehydration rate during the step of forming a dehydrated melt composition in accordance with the invention.

Refering to the drawings, lines A and B in FIG. 1 indicate the lower and upper critical levels of the temperature, respectively. Lines C and D in FIG. 2 indicate the lower and upper critical levels, respectively.

If the present process is carried out under conditions other than the specific conditions stated above with respect to factors (1) to (6), it inevitably causes hydrolysis of fatty acid esters, and a remarkable increase in the viscosity of the system with the result that sucrose esters and of fatty acid are produced in a poor yield.

For example, if the material sucrose and fatty acid ester are employed in an amount outside the above described specific range, hydrolysis of fatty acid ester takes place two to three times as much as it does when the amounts are within the specific range.

If the system is heated up to to C. above the upper limit level of the above specific temperature ranges during the step of forming the melt composition this will cause hydrolysis of fatty acid esters resulting in an increase in saponification rate up to -20% and a decrease in the transesterification reaction rate to approximately 50% or below. In some cases, the system becomes heterogeneous with the result that substantially no reaction is carried out.

On the other hand, if the system is heated to a temperature 5 to 10 C. below the lower limit level of the specified temperature ranges, the reactants in the system tend to be solidified with the result of an increase in the viscosity of the system several to several hundred times higher. Also, a heterogeneous reaction occurs with a considerable reduction of the reaction rate.

Fatty acid esters suitable for use in the process of this invention are esters of fatty acids having 8 to 22 carbon atoms with an alcohol which may be selected from the group consisting of methyl, ethyl, propyl and butyl alcohols, ethylene glycol, propylene glycol and butylene glycol, glycerol, sorbitol and pentaerythritol. Particularly, esters with alcohols having a low boiling point such as methyl, ethyl and propyl alcohols are preferred in producing sucrose esters of fatty acids having a high purity.

-It has been found that according to the process of the invention reaction of producing sucrose esters of fatty acids is scarcely taken place during the step of forming the dehydrated, homogeneous melt composition. If any, it is so slight as to be ignored.

Subsequent to the completion of making the dehydrated, homogeneous melt composition of reactants, the system is maintained at a temperature between 110 and 175 C. under atmospheric pressure or preferably under a reduced pressure within the range of 60 to 0 mm. Hg to thereby carry out the transesterification reaction for producing sucrose esters of fatty acids.

According to this invention, the above reaction treat-- ment subsequent to the formation of the melt composition is continued only for a short period of time ranging from 15 minutes to 3 hours during which the trans esterification reaction is completed with a high yield.

It is desirable from an industrial viewpoint to carry out the transesterification reaction in direct succession to the making of the melt composition in the same reactor. However, it is also possible to conduct the two steps separately and in dilferent, independent devices.

A control over the amount of monoester contained in the product sucrose ester of fatty acid is generally eflected by adjusting the molecular ratio between sucrose and fatty acid ester to be used in the reaction. The ratio between sucrose and fatty acid ester being the same, the process of the invention enables the production of sucrose ester of fatty acid having a higher monoester content than that obtain with conventionally known processes wherein an organic solvent is used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better and complete understanding of this invention, typical examples thereof together with some comparative examples are shown in the following:

Example 1 In a 350 l. reactor, 50 kg. of sucrose and 25 kg. of sodium stearate were placed and a homogeneous mixed solution thereof was prepared with the addition of 25 kg. of water. A substantial portion of the added water was removed at an elevated temperature of the solution between and C. and 1.0 kg. of K C0 was then introduced into the system. Thereafter, 25 kg. of methyl ester of beef tallow fatty acid was added while the remaining water was benig gradually removed at an elevated temperature of C. under a reduced pressure of 60 mm. Hg.

Subsequent to the completion of addition of methyl ester of beef tallow fatty acid, the system was maintained at an elevated temperature of 150 C. and under pressure of 60 mm. Hg for 3 hours to thereby obtain 96.5 kg. of a reaction product.

It was found that 95% of the added methyl ester of beef tallow fatty acid was converted to sucrose ester of fatty acid as a result of the transesterification reaction. The composition of the sucrose ester after purification was determined by a thin layer chromatographic analysis as follows:

The saponification rate of the final product was 5%.

Example 2 2 kg. of sucrose and 0.75 kg. of sodium stearate were dissolved in 1 kg. of water in a reactor to prepare a homogeneous solution of the mixture thereof. To this mixture 0.75 kg. of methyl ester of beef tallow fatty acid and 20 g. of KOH catalyst were added while raising the temperature of the mixture from 80 to 150 C. and reducing the pressure to 50 mm. Hg to dehydrate. Thereafter, it was kept at a temperature between 150 and C. for 30 minutes to obtain 3.2 kg. of a reaction product.

85% of the added methyl ester of beef tallow fatty acid was found to be converted to sucrose ester of fatty 1 acid by the transesterification reaction. The composition of the sucrose obtained after purification was determined by a thin layer chromatographic analysis as follows:

The saponification rate of the final product was 7%.

Example 3 35.8 kg. of sucrose, 18.7 kg. of sodium beef tallow of fatty acid and 35.0 kg. of water were placed in a reactor to prepare a homogeneous solution of the mixture thereof. To this mixture, 15 kg. of methyl ester of beef tallow fatty acid and 716 g. of K 00 as the catalyst were added while elevating the temperature of the mixing from 80 to 150 C. and reducing pressure to 50 mm. for dehydration. After the addition of another 30.5 kg. of methyl ester of beef tallow fatty acid, the mixture was kept at a temperature of 145 C. and under pressure of 50 mm. Hg for 3 hours to thereby obtain 92.5 kg. of a reaction product.

90% of the used ethyl ester of beef tallow fatty acid was found to be converted to sucrose ester of fatty acid as the result of the transesterification reaction.

The composition of the sucrose ester obtained after purification was determined by a thin layer chromatographic analysis as follows:

The saponification rate of the final product was 12.5

7 Example 4 1.5 kg. of sucrose, 660 g. of sodium beef tallow fatty acid and 2.0 kg. of water were placed in a 10 l. reactor to prepare a homogeneous solution of the mixture thereon. To this mixed solution, 1.0 kg. of propylene glycol monostearate and 30 g. of KOH as the catalyst were added while it is heated up to a temperature between 110 and 150 C. under a reduced pressure of 3 mm. Hg to form a dehydrated melt composition. Thereafter, it is put through a transesterification reaction at a temperature between 155 and 160 C. under a reduced pressure of 3 mm. Hg for 90 minutes to thereby obtain a reaction product.

The obtained product contained 43.5% of sucrose ester of fatty acid and it was found that 82% of the used propylene glycol ester reacted with sucrose.

The composition of the obtained sucrose ester of fatty acid was as follows:

Percent Monoester 56.3 Diester 31.4 Triand polyester 12.3

The composition of the residual propylene glycol ester The saponification rate of the obtained product was 23.7%.

Example 48.8 kg. of sucrose and 25 kg. of sodium beef tallow fatty acid were dissolved in 60 kg. of water to make a homogeneous solution of the mixture thereof. 27.4 kg. of hardened oil of beef tallow and 1.0 kg. of K CO were added to the solution at an elevated temperature between 100 and 155 C. and under a reduced pressure of mm. Hg to form a dehydrated melt composition. The melt composition was thereafter put through a transesterification reaction at a temperature of 160i2 C. under a reduced pressure of 5mm. Hg for 2 hours to obtain a reaction product.

The reaction product contained 36.2% of sucrose ester of fatty acid and 9.1% of glyceride. 70% of fatty acid in hardened oil of beef tallow used was reacted with sucrose.

The composition of the obtained sucrose ester of fatty acid was as follows:

The saponification rate of the obtained product was 28.7%.

COMPARATIVE EXAMPLE 1 This is a comparative example wherein water was not used as the solvent. 2 kg. of sucrose, 60 g. of potassium methylate, 0.5 kg. of potassium stearate and 0.5 kg. of methyl ester of beef tallow fatty acid were placed in a reactor having a capacity of 10 l. The mixture thus prepared was heated to an elevated temperature of 150 C. under a reduced pressure of 10 mm. Hg for 7 hours to thereby obtain 2.85 kg. of a reaction product.

It was found that 83% of methyl ester of beef tallow fatty acid used was converted into sucrose ester of fatty acid by the transesterification reaction. The composition of the obtained sucrose ester after purification was determined by a thin layer chromatographic analysis as follows:

Percent Monoester l2 Diester 30 Triand polyesters 52 COMPARATIVE EXAMPLE 2 This is another comparative example wherein the dehydration at an elevated temperature was omitted.

A mixture comprising 2 kg. of sucrose, 1 kg. of sodium salt of hardened beef tallow fatty acid and 1 kg. of methyl ester of beef tallow fatty acid were uniformly dissolved in a kneader. After adding 20 g. of K CO the mixture was dehydrated at a temperature between 60 and C. under a reduced pressure of 50 mm. Hg. Upon the complete removal of water, the mixture was then heated up to an elevated temperature of C. while stirring and keeping under the same conditions for 3 hours to thereby obtain 3.7 kg. of a reaction product.

83% of methyl ester of beef tallow fatty acid was found to be converted into sucrose ester of fatty acid through the transesterification reaction. A thin layer chromatographic analysis of the obtained reaction product after purification showed the following composition:

Percent Monoester 48 Diester 32 Treester 20 The saponification rate of the product was 21.5%.

What is claimed is:

1. A process for synthesizing sucrose esters of fatty acids, which comprises (a) preparing a solution of water, sucrose and a fatty acid soap selected from the group consisting of potassium, sodium and calcium salts of fatty acids having 8 to 22 carbon atoms, the sucrose being completely dissolved in the solution,

(b) adding to the solution of (a) an alkaline catalyst and a fatty acid ester selected from the group consisting of esters of fatty acids having 8 to 22 carbon atoms with an alcohol selected from the group consisting of methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol, propylene glycol, butylene glycol, glycerol, sorbitol and pentaerythritol, under temperature elevating and pressure reducing conditions so as to avoid hydrolysis of the fatty acid ester and form a substantially completely dehydrated, homogeneous melt composition, and

(c) carrying out a transesterification reaction between the sucrose and the fatty acid ester in the melt composition at a temperature of 110 to C.

2. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which said step (c) is carried out under a reduced pressure below atmospheric pressure.

3. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which a minor amount of said fatty acid ester is added to said melt composition at said step (c).

4. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which said fatty acid soap is used in an amount of 5 to 40% by weight with respect to the total amount of the sucrose and fatty acid ester.

5. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which said solution prepared at said step (a) contains water in an amount within the range of 10 to 200% by weight with respect to the total amount of sucrose and said fatty acid soap.

6. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which the weight ratio of sucrose to fatty acid esters is within the range of 80:20 to 5:95.

7. A process for synthesizing sucrose esters of fatty acids defined in claim 1 in which the catalyst is selected 9 from the group consisting of hydroxides, carbonates, bicarbonates, methylates, ethylates and propylalcoholates of potassium, sodium and lithium.

8. A process for synthesizing sucrose esters of fatty acids as defined in claim ,7, in which said catalyst is used in an amount of 0.1 to 10% by weight of the amount of the sucrose. a

9. A process for synthesizing sucrose esters of fatty acids as defined in claim 1, in which the temperature and the pressure at the end of said step (b) are within the ranges of 110 to 175 C. and 60 to 0 mm. Hg, respectively.

10. A process for synthesizing sucrose esters of fatty 10 acids as defined in claim 2, in which said step (c) is carried out under a reduced pressure within the range of 60 to 0 mm. Hg.

References Cited UNITED STATES PATENTS 2,831,855 4/1958 Martin 260-234 R 3,248,381 4/1966 Nobile et al. 260234 R 3,249,600 5/1960 Nobile et al. 260-434 R 10 3,558,597 1/1971 Von Brachel et al. 260-234 R JOHNNIE R. BROWN-E, Primary Examiner 

